The present invention relates to an inter-frame decoding system for television signals and more particularly, to an inter-frame decoding system wherein a frame in which an error is detected is replaced by the preceding frame stored in a frame memory.
An inter-frame encoding/decoding system compresses the transmission band width by transmitting an estimated error only, with a decoded digital television signal of a preceding frame as a predicted value. This requires for reproduction that the predicted value produced by an inter-frame encoder be in agreement with the predicted value of an inter-frame decoder. When a decoded error has occurred in the digital television signals decoded by the inter-frame decoder due to a transmission error, the error remains in the decoded digital television signals unless it is corrected by some method. Therefore, the detection of a transmission error, or the detection of the fact that the predicted value of the decoder is different from the predicted value of the encoder, is important in the inter-frame encoding/decoding system.
An inter-frame decoding system capable of detecting such a transmission error is described in U.S. Pat. No. 4,677,480. This prior art system, however, does not solve the problem of how to cope with the situation after a transmission error has been detected. One of the prior art techniques to cope with the decoded error is that until the transmission error disappears, the picture of the same frame in which an error has been detected is repeatedly read out from a frame memory which stores an inter-frame decoded signal. Another prior art technique is that upon detection of the transmission error, the output picture is made blank until the transmission error disappears. However, the former technique has the disadvantage that the picture containing the error is continuously displayed, while the latter makes the picture unpleasant to the viewer because of the discontinuance of the display.